1. Field of the Invention
This invention relates to compounds, to processes of their preparation, to pharmaceutical compositions containing them and to their medical use as agonists at kappa opioid receptors.
2. Reported Developments
Opium and its derivatives are potent analgesics that also have other pharmacological effects, and exert their effects by interacting with high-affinity receptors. It has been shown by investigators that there are at least three major opioid receptor types in the central nervous system (hereinafter CNS) and in the periphery. These receptors, known as mu (.mu.), delta (.delta.) and kappa (.kappa.), have distinct pharmacological profiles, anatomical distributions and functions. [See, for example: Wood, P. L., Neuropharmacology, 21, 487-497, 1982; Simon, E. J., Med. Res. Rev., 11, 357-374, 1991; Lutz et at, I. Recept. Res. 12, 267-286; and Mansour et at, Opioid I, ed. Hem,. A. (Springer, Berlin) pp. 79-106, 1993.] The .delta. receptors are abundant in CNS and mediate analgesia, gastrointestinal motility and various hormonal functions. The .mu. receptors bind morphine-like drugs and mediate the opiate phenomena associated with morphine, including analgesia, opiate dependence, cardiovascular and respiratory functions, and several neuroendocrine effects.
The .kappa. receptors have a wide distribution in CNS and mediate a spectrum of functions including the modulation of drinking, water balance, food intake, gut motility, temperature control and various endocrine functions. They also produce analgesia. [See, for example: Leander et at, J. Pharmacol. Exp. Ther. 234, 463-469, 1985; Morley et at, Peptides 4, 797-800, 1983; Manzanares et al, Neuroendocrinology 52, 200-205, 1990; and Iyengar et at, J. Pharmacol. Exp. Ther, 238, 429-436, 1986.]
Most clinically used opioid analgesics such as morphine and codeine act as .mu. receptor agonists. These opioids have well-known, undesirable and potentially dangerous dependence forming side effects. Compounds which are .kappa.-receptor agonists act as analgesics through interaction with .kappa. opioid receptors. The advantage of these agonists over the classical .mu. receptor agonists, such as morphine, lies in their ability to cause analgesia while being devoid of morphine-like behavioral effects and addiction liability.
A large number of classes of compounds which act as agonists at .kappa. opioid receptors have been described in the art including the following illustrative classes of compounds.
U.S. Pat. No. 4,065,573 discloses 4-amino-4-phenylcyclohexane ketal compounds having analgesic activity.
U.S. Pat. No. 4,212,878 discloses phenylacetamide derivatives having analgesic properties and reduced physical dependence liability properties, relative to morphine and methadone.
U.S. Pat. No. 4,145,435 discloses N-(2-amino-cycloaliphatic)-phenylacetamide compounds having analgesic activity and narcotic antagonist activity.
U.S. Pat. No. 4,098,904 discloses N-(2-amino-cycloaliphatic)-benzoamides and naphthamides useful for relieving pain.
U.S. Pat. No. 4,359,476 discloses substituted cycloalkane-amides useful as analgesic and having low abuse liability.
U.S. Pat. No. 4,438,130 discloses 1-oxa-, aza- and thia-spirocyclic compounds having analgesic activity, low physical dependence and abuse liability properties and little dysphoric inducing properties.
U.S. Pat. No. 4,663,343 discloses substituted naphthalenyloxy-1,2-diaminocyclohexyl amides as analgesics.
U.S. Pat. No. 4,906,655 discloses 1,2-cyclohexylaminoaryl amides having high kappa-opioid affinity, selectivity and potency and useful as analgesics, diuretics, anti-inflammatory and psychotherapeutic agents.